Method for preventing corrosion



Aug. 17, 1943. R. PoMERoY METHOD FOR PREVENTING CORRSION Filed June l0, 1940 TNB FIRM A Tro RM1-Ks.

Patented Aug. 17, 1943l 2,326,968 y Mlrrnlo'nFORrmfENTrNG'ooRRosIoN y l MRi chardPomel-"ony; Harbor City, Calif., lassigno-rlof l* Hone-halfto Fred Bowlus, Whittier, Calif. y' l 'f -Aplication V.ruine-10,1940, serial No. 339,7` (ci. alii-58V l. U Y .Y v V55fClarnS This invention relates to the maintenance of;

contact a gaseous atmospherel of such-character as to directlyfor indirectly lead tothe corrosion of structural surfacesin contact withxsaidatsewers and similar;structureswhich encloseor mosphere; and relates' more particularly'to fa". method and device for the-continuedneutralizationof ,corrosive acidsin said atmosphere .and/or onsaid exposed sur;taces.-.` f

In a sewer system, '-the ow ofi` liquid sewage normallyl'constitutesfarstream having a cr'oss f section only a fraction"of thatiof .the sewer.

The remaining spaceisioccupiedfchiefly -by.air;

which has access to the sewer at manholes, vents,

etc. Y In instances where the sewer is constructed of a material such as concrete, which is.susceptible to corrosion by acids, continued service isfoun'd to give rse-to extensivedestruction of surfacesv which are in Contact with'thev enclosedfatrnos-r` phere. Forexample, a reinforcdconcrete pillar forming part of a manholestructure was found after four years service-to have beenjreduced to abouthalfof its crossr section; by Aatmospheric e.

corrosion, yboth the concrete and-thereiforcing corrosion.` Samplesopasty disintegrated 'con` crete from this and neighboring structures showeda surprisingly high sulphuricacid cori-- tent, as high as 7% based'on the' moisture con'- tent.-y 1

I believe that these effects lution, of gases from theisewagef-.which igases,

are due tothe evof either in their original -form'orasv subsequently modified, are responsible for the observed acidic corrosion. I i

Theliquid sewageitself is rarely acidic and is, for the most partgneutral vor slightly,- alkaline.

As a result of changes naturally occurring in l,

sewage however, this liquidgis*continually giv-jj ing oi gases, includingacidic gases suchas' CO2 vand HzS. Some of theobserved corrosion mayV be due to the direct action lof these gases. the case of H28, moreoverjfextensive oxidation,

apparently through themedium of aerobic bac-v teria located on the exposed wall surfaces, leads to the formation of much strongernacidssuch as YH2504. The extent of this, process f may be judged'from the case of anine and one-half. foot.-

sewer in whichfextensive tests showed that Vover 6000 poundsof sulphuri'c acid-Were formed in each I nile of sewer per year. v

Various methods havebeen proposedfor Vsulphide control'of sewage, including chlorination,

treatment with metallic salts, etc.VY These methods'are designed to reduce the sulphide ionlcon'a centration of the sewage, and ifthis.concentrati;v

tionis brought sufliciently low, the corresponding vapor pressureV of HzSfmaybefinadeneglifY 5 There are, however,v twogmajorv defects in the use of such-methods'for controloffy atmosgible'.

pheric corrosion.

The first difcultyarisesfromthe fact v that a Vsubstantial vvsulphide ion; vconcentration develops. again quite rapidlyrsubsequent toy treatment and, hence, atreatingstation'vat the beginning oa two or three milestretch-of sewer may have .little or no eiect on corrosion atthe lower end of the sewer.

andineiciency and-arises from the-fact that the HzS evolvedinto thea-tmosphere of the sewer represents only la.nuinlltc ira CLOILO thssulphidf;

content of the'liquid sewage, Consequently, the

conventionalchemicaltreatrnent of the sewage requires far more chemical reagent than would Ybe required for the control of the evolvedmHzSwere the YlatterA isolated.`

It is anrobject ofthe present inventioitlV to 4pro,-

25xfvide a method and device fforvthe control of a t- Y mospheric vcorrosion invsewers and similarcori-I duits( enclosing gases which; are corrosive to exposed surfaces, andfor theprotection of structuresv generally which have surfaces exposedl te:A

an acidic ofacid-eng'endering atrnosphere.,.

Y It is afurther object of the present`V invention.. to'vprovidea method and apparatus for the heulV tralizationof corrosive-acids inthe atmosphere Aorfonexposed surfaces in theintericr of a sewer.Y

or other conduit, andfurther, toprovidea meth'.'

od of the kind described which aifords assuredfff protection .throughout the entire systemwhich itis v`desired to protect, and which is 4relatively cheap and efficient and which is directed prifv marilyto treatingthe immediate source of*` the` Vcorrosion diinculty, namely,- the acids in the at xnospherelor on the Asurfaces exposedv thereto', rather than to treating the niuch'greater :nass ofV sulphide in the liquid sewage,

Thesedobj'ects are attained in accordance with the presentinvention byV injecting an-,alkaline fluid, preferably gaseous ammonia, into. the atmosphere ofthe sewer or conduit, preferably at anurnberof points, or into alcorrosive atmos-'I phere inthe vicinity of vexposed surfaces which' 'it is desired to protect. Y. u 4

Further objects and aspectsf of the. invention will'become apparent in the following discussion,

made with'particular referencetotheattached Y y drawing, in which:v Y*

A pipe I5 is suspended from the top of the V.

vsewer by means of brackets i6 and carries aVV number of injection nozzles or orifices-'H adapted'H to inject a pressured neutralizing uid into the The orifices or nozzles Il may be ofany suit-4 able design, one specific form being illustrated" sired accuracy. The discharge points are positioned at intervals sufli'ciently close that the zones of protection around each injection point will to some extent overlap, thereby insuring ade quate proteotion'throughout the sewer. The size of the individual zones will depend upon, among other things, the rate of HQS evolution by the sewage or the rate of sulphuric acid 'formation on the'walls of the sewer, the rate at which ammonialis injected into thesevver'atnwsphere, and upon conditions naturally present in the sewer and controlling the rate of diffusion and/or vcone yection of ammonia throughout the atmosphere l maiukmtelyto the surfaces which it is :de-

' atmosphere of the sewer for 'protection of"VA exposed surfaces, such as the interior wall surl face|3. l

siredto protect. V

There may Vbe some neutralization in the gasevous phase 4to forni ammonium carbonate, arnand similar salts, although in which. shown. fitted itrtothe general run of pipe t5 by means of unions. Mandi' 12, although ordinary couplings may'l be used if desired therefrom both externally and` internally... A rubber Vsleeve 2# isvmountecV on. the! external prog iecti'o-Irorr tube 23 and serves asa" connecting means toa glass capillary 25, the length and bore of the capillary Z5 being calibrated togive desired rate offflow of injected' neutralizing nue-V dii-rm.

Under most conditions of service, such smallV quantities of neutralizing ilu-id are 'required that Sed tion '2i-is providedwitha short tube' 2,"3V which'. i transpierces thewall ot the'pipe 2E andprojects suona vfluidi is best injected iin' diluted form.` Fer' example, wherega-seous ammonia is employed as a neutralizing agent, it'ma-y be diluted withcoin-l pressed air'.

-Equi-pmexrt-y suitable for suppi'ying the pipel5 with a mixture or compressed air and gaseousrammonia is shown in Figure 1, and com? l prises' an ammonia gas-supply tan-k 3U equipped with apressure reduction valvel' 'le'acingeintoV the ammonia flow-line 32 provided with a lflow indicator 33. VA valve 34 isprovided in 32L to 'regulate thenow-therein. 'mie pipe e2 empties into a'pipe'4 4'6- to which'Y is suppl'ieefcom pressed air by meansY conm/rising a blower AIl arid an electric motor" $2'. Theadirrxed air andiam' monia are passed through aflow meter Llenar a pressure gauge 44: is provided to indica-tothe pressurein line 4:3. `VThe' pri-pedo serves as a feed shown but vwhich maygconvenienjtly' include a pipe means descending through a'mar'rholeL or other conventional; opening in the sewer #9.

order to maintain the desired pressure if! the pipe' l5,1the far-end thereofi's rnalirrt',,airre'vlv closed for the pipe l5 by mean-s of connections not f'ulliy v :most instances the concentrations involved will be so low that the acidic and alkaline components of the atmosphere will remain dissociated` Either the ammonia om salts serve as arr active. neutralizing agent 'mr strong :underminever..` A; a result, any sulplrmic acid present-o1' formed on or in. the Wall` minces; auch asthe surface oi'`n"ig.4 1V willi bef rapidly' neutralized by the-,absorption ot ammonia or v'axrrnmomx'cal compounds with; the formation of suieA phate which is much less` detrimental 'tof the structure the unneutraltzedl sulphumtc acid, Similarly, tlpresence. of ammonia tends to crease'any :corrosivev action` me` to .the presence f of hydrogen sulptde, campania' acid, or other gaseous acids'M Y Various modifications of the described embodiments and methods may bemade, including those speciicallly .mentioned irr the Ioll'owing':

Various fluids having an alltalfmel reactions may be employed izo:l the protection of thel sewer in accordance with 'my process.. Jn' generar, it. is.

preferable tarempicy a gaseous mnd and to make" use of gaseous' neutralizing agents,Y suchas amr-- momia ormethyl'azmm. Also, I may empio-y lfq;

uid havrngvsumcient vapor pressure-toremainvolatile. atjthe concentrations errrpleryedf.`

such, neutralizing agents are best di.-

lut'edibsf'1 an inert gas; such as nitrogen, vor

therme;

I. may: also employ water-semble aFltaline-materms anzidv use an aqueous solution thereof for injection into the sewer. In such instances, the' in-jecticnnozzlses are best'. anfangedto spraydirectlyion. the. walt surfaces which it. is desiredv to protect.' or to produce.v a. uelydispersed fog or to and collect on the 'cxt-V posed surfaces. l

In. the instance of a new sewer' or other struc;

' ture mwhicirfomatm. of corrosive manor and, if the pipe i5' is of slrlrfstari-tialg length, .the

down-stream portions thereof maybe considerably reduced in diameter in accordance with the# lessened'ilo'w requirements in that portion-- of the system.

The operation of this device is as follows 'z5 flow of ammonia from the tank 39 is adjusted to that value whichl is deemed 'adequate or' nec-- essary for protectionl forV the lengthfof' sewer Vserviced bythe pipe f5. In general, this rateWil-I atleast equal theV rateol sulphuric acid produc-..

tion in the sewer and', for' best results, `should be several times its value. 4 Y

When thefquantityv ammonia thus employed yet. takerV1 piace: on. the exposed surfaces, the. alkalinizatton et the surface may be unnecessary, in which case it may sufcemerely to neutralize .or absorbtheihydrogen lsulphide present. in the atmosphere. Under these' y sinful-mstannees, a spray Y of alkati'rre liquid' may beremloyd without. the

is relatively smalhit is 'diluted with air toch tain a volume Whichcan' be handled and-infected at the plurality of injection points-v'rvithlmedewV Yrequirermee-t"-'tlilat-it. impinge om the surfaces.

which it iis desired to protect, I

Various- .types of. :rosales or. minces maybe ern-.- ployeo'. and their" dispositionk may` be other. than thatV illustratedin Fig. I. formnrple,

or laterally proooctingnozzlaes maybe employed insteadE of the downwardly depending nozzlesas shown in Fig. 1, or the structure movinV may be ree-oriented'. by axial rotation. relative tu the; union couplings. Also, the supply pipe l!! maybe pg sitioned -atvarious points .within the. sevenor Y Y infthe walls ofthe 'sewenand'in:sorneinstances Y may Vtze-laid external to the sewer with outlets running into the interior ofthe sewer. :y Y Frequently a portion-ofthe sewer will be subject to more severe corrosion than otherportions and, inthe vicinity ofsucli-a point, Ifmay--provide either a' closer v's'pacingof nozzles or employ nozzles of larger orice,-or both,'to insurean adequate supply of a neutralizing Aagent infsuch'v a region of severe corrosioni Where very extendedflengths of pipe are employed, it is also frequently desirable-to decrease the spacing interval or to increase the size of the orifice, or both, toward the down-stream end of the pipe in order'to counteract the effects of presin -which such cables-'Amay be laid. Such corro-V.

sure reduction attendant the Ypassage of fluid through an extended length of pipe.

Where var very extended installationY is contemplated, it may be some times advisableto provide duplicate installations for successive lengths of sewer. Each installation, however, will normally be able to protect several miles of sewer. In one typical design, a three-mile length of ten foot sewer is protected by a single runof pipe tapering 'from a diameter of 2Vwhere the air and.v

ammonia enter and to a diameter of 1/ at the far end. Outletsand nozzles are spaced'at 20 cables is exposed to the atmosphere of. tunnels sion has beenvariously attributed to theaction of carbonfdioxide and to theactionofoxidesof nitrogen produced by bacterial action. -In any case, thefcorrosive agent is essentially acidicy .and `may-be readily neutralized lbyfpracti'se lof-'the present invention to .giive adequate protection of.r

thke'flead 'cables Iand similar 'exposes surfaces. '."Iclaimeas my invention: if

LA method of preventing acidic corrosion of surfaces in sewers and which surfaces are exposed to the gaseous atmosphere labove a stream of sewage .flowing in said sewer, without'treatment of the bulk of said sewage to reduce .the sulphide content thereof, which method includes the steps of introducing-into said gaseous atmosphere a gaseous neutralizing agent capable of reacting with sulphuric acid tending to form o-n said surfaces exposed .to said gaseous atmosphere; and controlling the amount of said gasecus neutralizing agent thus introduced to supply sufficient-of said gaseous neutralizing agent to lsubstantially neutralize the sulphuric acid tending to form on said surfaces during continued `flow of said sewage along said sewer.

foot intervals, and an adrnixture of air .and'arnmonia issupplied the pipe at a pressure of about i lb./sq.inch, the rate of` air now being about 8 cubic feet per minute, and the rate of ammonia ow being about 2 cubic feet per minute.

In some instances it is necessary vto protectf For exarnonly individual points in the sewer. ple, the problem of corrosion may beencountered only in the Vvicinity ofa manhole in which structures are present causing agitationof the flowing sewage with attendant ylocalizedrevolu- A tions. In such situations, themeans for applying the ammonia will be substantially simpler` Y than that described above and need not comprise more than a tank of anhydrous ammonia, a con- 'trol valve through which the ammonia can be allowed to escape slowly, and a tubingadapted to conduct the stream of ammonia to a suitable place of release in the vicinity of the structure subject tov such localized corrosion.

In instances where the sewer is ventilated by 2. A method of preventing corrosion of sur-` faces in sewers and which surfaces are exposed tothe gaseous atmosphereabove a streamof sewage lflowing in vsaid sewer,v without treatmentof `the bulk of said sewage-to reduce the sulphide content thereofv to such an extent as tok prevent A,theappearance of sulphuric acid on said surfaces, which method includes the steps of introducing into said gaseous atmosphere at a pluralityof positions spaced along a length of said sewer a gaseous neutralizing agent capable of reacting With sulphuric acid .tending to form on said surfaces exposed to vsaid gaseous atrnospheie,` the total amount of said gaseous neutralizing agent being sufficient to neutralize said sulphuric acid forming on said surfaces in said length of said sewer during ow of vsaid sewage therethrough. Y.

3. A method as dened in claim 2, Vin which said gaseous neutralizing agent comprises gasecus ammoniaand air.

fl. A method of preventing corrosion of rsurfaces in sewers and which surfaces comprise concrete and are exposed to the gaseous atmosphere above a stream of'sewage flowing in said sewer, said sewage being substantially non-acidicbut acting to give `off hydrogen sulphide during its V flow along said sewer, said hydrogen sulphide bea forced draft of air, the length of sewer swept Y n,by such a draft may be protected by the addition of an alkaline gas,` such asammonia, to

the air entering the'sewer. y

In some instances, periodic, as contrasted with continuous, injectionof the ammonia may suffice Vto prevent acids accumulating on exposed 'surfaces from reachinga dangerous concentration.

For example, the ammonia may be released in quantities sufficient to insure neutralization of the exposed surfaces atv hourly or daily intervals, depending upon the specific conditions present.

While I have described my invention with particular respect to conditions obtaining in sewers, it will be obvious that the methods and equipment employed may be used with equal eiiicacy in pipe galleries, tunnels, enclosedpassageways,

and Vin similar structures in which an acidic corrosive atmosphere may bepresent. For example, serious corrosion of lead cables carrying electric ing oxidized on said surfaces to ,produce sulphurio acid, which method includes the steps of:

introducing into said gaseous atmosphere of said sewer at one position an amount of gaseous ammonia suiicient to neutralize the sulphuric acid tending to form on said surfaces in a zone'adjacent said one position; andintroducing into said gaseous atmosphere at another position downy stream from said one position an amount of gaseous'ammonia sufcient toneutralize lthe sulphuric acid tending to form on said surfaces in a zone adjacent said other position, said positions being suiciently close to each other so that said v zones will overla-p'to produce substantially cornplete neutralization of the sulphuric acid tending to form on said surfaces between said positions.v

5. A method of preventing corrosion of sur- I faces in sewers andwhich surfaces are exposedto the gaseous atmosphere above a stream of sewage flowing in said sewer, said sewage acting t-o give on hydrogen sulphide during its ow along `wires is'often noted when'the lead sheath of such saidasewer; hmmfgsrrurhide beine om on saidi-smfacesm produce sulohurie acid, the amount o saidf hxdsogemsulphhie evaiutian inf creasing ,with an: mrminiturhmeme @E sa.

awi'im sewage, said sewage flaming: more tum buientiy ait one -posiin than ab yarmlaer., whieh method. malades; the stepsof: mistaking; said surfaces the: vicinity/@fwd positbmesf greaiier,

acid an; said surfaces by intzmxiiicingV gaseous am ma. im said; gasexzus ammosphmjeadjgcent said positionk the amount and rate of introduc-A .tirm of. said; Hameau@L Aaxnlrlnaf being correlated with thvvaeg af.; acid formation. on said surfaces 'm 'said vicinity to supply several.vv times the amount ofi gaseous ammonia., required tu neu-- tralizethe sulphavlmicA acid iomned-l on said sur-- faces il: veini-ty `of said position.

Y PQMEROY. 

